Teenager Jake Fahri was given a life sentence with a minimum of 14 years today for killing schoolboy Jimmy Mizen.
Jimmy, a church-going 16-year-old, died after Fahri went berserk in a local bakery and threw an oven dish at him.
It shattered on his chin - sending a one-and-a-half-inch shard of glass into his neck, where it severed vital blood vessels.
Fahri, 19, was found guilty of murder at the Old Bailey after the jury had been deliberating for just over a day.
He had pleaded not guilty and claimed he had been acting in self- defence.
Jimmy's large family applauded as the verdict was delivered but they soon fell silent, weeping and comforting each other.
Fahri showed no emotion as he was sentenced, but as he was taken to the cells he called out: "I will be all right, mum, I'll be all right" to his weeping mother in the public gallery.
Mr Justice Calvert-Smith said: "A trivial incident over absolutely nothing in a High Street bakery ended three minutes later with the death of a blameless young man."
He said that although Fahri had two clear opportunities to walk away from a row in the shop, he went back to cause serious harm to Jimmy who he felt had "disrespected" him.
He told Fahri: "You carried out your intention so successfully that you killed him, depriving a loving family of a son and brother."
The incident had terrified staff in the shop, Jimmy's brother Harry and a customer.
But the judge added: "The court accepts you did not intend to kill your victim and that you are a very young man."
The judge praised the Mizen family for the dignity they showed in court and for the "clear and moderate" way in which they had worded their impact statements to the court.
Sally O'Neill, QC, defending had told the court that the incident at the Three Cooks Bakery in Lee, south London, on 10 May last year, had been "deeply unlucky".
"It was clearly something which happened on the spur of the moment. The dish was picked up because it was there," she said.
Jimmy had celebrated his 16th birthday the day before his death.
The court was told that blood squirted from Jimmy's neck and covered the shop like a scene from a horror film.
Jimmy staggered into a back room where, 15 seconds later, his older brother Tommy, 27, found him.
He collapsed in Tommy's arms. Their mother Margaret arrived and fainted. She sent for a priest when she came round.
As Jimmy was hit by the glass, Fahri swaggered from the shop with a triumphant grin on his face, according to witnesses.
Fahri, from Milborough Crescent, Lee, had not wanted to lose face after picking a row with Jimmy, who was described by friends as a gentle giant.
Jimmy had stood his ground when Fahri had rudely demanded he get out of his way in the shop.
His anger grew as Jimmy's brother Harry, 19, suggested he say please.
And he exploded with rage when Jimmy, 6ft 2in and 14st, refused to go outside the shop when 5ft 7in Fahri challenged him.
He went back in and hit Jimmy with two plastic drinks bottles and was further humiliated when the brothers punched him and all three crashed into a glass cake display, before he was bundled out of the shop.
Fuming, Fahri picked up a metal-framed advertising sign and stormed back in after kicking the glass in the door.
Poking Jimmy with the sign, Fahri panicked when the schoolboy grabbed hold of it and was about to pull it out of his hands.
He grabbed the hot dish containing sausages from the counter and threw it in front of him.
Crispin Aylett QC, prosecuting, said: "A trivial incident, brought about by the defendant's rudeness, escalated into something horrific.
"The defendant reached for any and every available weapon with which to attack the Mizen brothers.
"The whole incident lasted no more than three minutes - three minutes of absolute madness on the part of this defendant."
Fahri told the court he did not mean to do serious harm.
He said: "I did not think it would break, let alone hit him in the face. I literally picked it up and slung it in two seconds."
Fahri had been in and out of trouble at school for incidents involving his loss of temper.
He had four previous findings of guilt at juvenile courts, two robberies, one burglary and a common assault on a girl.
After a spell at college, he helped his heating engineer father part-time. He lived near the Mizens with his parents and younger sister.
Jimmy had gone with Harry to buy his first lottery ticket on the Saturday morning.
The brothers had then gone into the bakery near their home to buy sausage rolls.
Jimmy was one of nine children in a loving family headed by Mrs Mizen, 56, and her husband Barry, 57, who ran a key cutting business.
Mrs Mizen said of Jimmy: "He was the loveliest, gentlest giant."
He attended St Thomas More Catholic comprehensive school in Eltham.
He had been due to start an apprenticeship with a local council in its housing and maintenance department after taking his GCSEs.
Mrs Mizen, 56, told the court in a statement: "He had lots of friends that were loyal, and he was loyal to them. He helped friends when they were being bullied.
"He would stand his ground and stand up for his friends. I recall our concern that it would get him into trouble one day."
Jimmy was "easy going" and was "always helping people".
He used to cut the grass for the family's 87-year-old neighbour and since his death, Mrs Mizen said, she and her husband had learned of other acts of kindness.
They were told that Jimmy would always give up his seat on the bus for the elderly and would sometimes buy a bag of chips for a local homeless man.
Jimmy's father Barry, 57, described his son as a "shining star" in a victim impact statement read to the court.
"He was polite, courteous and always seemed to be happy," he said.
"He enjoyed life. His loss is immense, not only to us but to all his friends and family.
"We are so proud to have been his parents. Jimmy was the shining star in our family and always will be remembered with a smile. God bless you, Jimmy."
Mr Mizen said he had "treasured memories" of Jimmy as someone who could get along with anyone and was "a pleasure to be with".
He said since the murder their youngest son George, nine, had been unable to sleep in his own bedroom.
Another daughter Samantha, 21, who has Down's syndrome, would now always say "come back" when any member of the family went out, he added - because Jimmy went out and did not return.
Detective Chief Inspector Cliff Lyons dismissed Fahri's tears and apparent apology to the Mizens during his police interview.
He said: "I absolutely reject it was remorse and so do the Mizen family.
"I think it is quite insulting - a tactical ploy.
"Jimmy Mizen was terrified and spent the last seconds of his life behind a closed door and that genuinely sickens me."
He said the dish was potentially a lethal weapon because it was heavier than a brick and was made of glass.
He added: "Jake Fahri is an aggressive young man who throughout his life continually demonstrated an inability to control his emotions and restrain his temper.
"As we have all come to know Jimmy was the exact opposite of Fahri; a peaceful, courteous person with only the best intentions."
He said murder was the right verdict.
"This was an unusual case and is the first known murder to have involved an ovenware dish as the murder weapon."
Outside court, Mr Mizen said Britain was rapidly changing from a place of civility and fairness to a "country of anger" but together people could stop it.
With his wife and youngest son George standing by his side, his voice cracked with emotion as he said: "I want to thank God for Jimmy, thank God for his life.
"It was a pleasure and a privilege to have been his parents.
"This country stands apart from other countries. This is a country of civility and a country of fair play, fairness, and a country of safety. We are rapidly losing that.
"We have become a country of anger, of selfishness and of fear. It doesn't have to be like this. Let's together try and stop it."
Detective Chief Inspector Cliff Lyons said outside court: "Jimmy Mizen was an immaculate and decent young man. That never really came out during this trial.
"He is a credit to himself and his parents. Barry and Margaret have shown tremendous dignity and grace during this whole case.
"Jimmy is an individual that I think we all would aspire to have a son like him. Jake Fahri is entirely different, he can only be described as a yob.
"He is extremely violent and the jury have returned a just verdict."
Mrs Mizen thanked fellow parishioners for praying with the family and preparing meals for them every day during the case.